Need help diagnosing a hum.

Tex

I am asking this for someone who bought an amp from me and I was not able to help him. When the amp is plugged in and hooked up there is a hum coming from the speakers. When the interconnects are not plugged in there is no hum. When they are plugged in to the pre there is a hum whether the pre is turned on or not. Also if you touch the end of the interconnects you get a hum. I had used this amp with no problems on two different preamps. This guy is using it with a Denon AVR3300 receiver but like I said, he gets a hum even when it is not turned on. He said he has tried two different cables. Any ideas?

ben62670

Some advice that i had recieved from other polkies is to try a 2 to 3 prong adapter so you can cheat the ground on the amp. If that doesn't work try to disconnect any cable tv signal wires and see if it goes away. Also I would try one channel at a time with the interconnects. What kind of amp is it?

Good luck Ben

ben62670

http://www.polkaudio.com/forums/showthread.php?t=46864

There is some real good advice here.

Tex

Thanks Ben, that might help. This is a Nakamichi PA-5. I will forward this information to him.

Tex

He said the adaptor worked. Thanks for the help.

dcoil

Wow, to fix a hum in a day is pretty good work! As a follow-up, I had a bad hum in my system, and was tracked down to a ground difference with my cable TV signal (as Ben suggested). I don't know if the 2 to 3 prong adapter would've worked for me. What did work for me was a Cable Isolator from Holland Electronics LLC. It looks like a small choke (1" x 3"), that goes between the cable TV coming and the TV. The cable (TV) coming from the wall attaches to the isolator, and then cable goes from the other side on to the TV.